Solid polymer dispersions and method for their preparation

ABSTRACT

Solid blends of rubbery polymers and amorphous or crystalline polymers, said blends being free-flowing at temperatures lower than the glass transition temperature or crystalline melting temperature of the amorphous or crystalline polymer, are prepared by intimate mixing procedures. In general, said mixing conditions include high shear conditions sufficient to convert polymer A to dispersed particles coated with polymer B and produce a free-flowing powder blend.

[0001] This application is a continuation-in-part of application Ser.No. 10/079,730 filed Feb. 21, 2002, which in turn is acontinuation-in-part of application Ser. No. 09/696,088, filed Oct. 26,2000, which in turn is a division of application Ser. No. 09/218,925,filed Dec. 22, 1998, now U.S. Pat. No. 6,194,518, which in turn is acontinuation-in-part of application Ser. No. 08/959,256, filed Oct. 29,1997, now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 08/742,536, filed Nov. 1, 1996, now abandoned,which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to polymer dispersions in solid form and amethod for their preparation. More particularly, it relates to thepreparation of polymer blends in solid form.

[0003] The use of elastomeric (i.e., rubbery) polymers as additives inblends comprising other polymers is known. Various rubbery polymers areuseful as impact modifiers, flame retardants and additives conferringother properties on blends in which they are incorporated. While thedispersion of liquid additives in polymeric powders is well known andpreviously documented by Dahms et al. (U.S. Pat. No. 3,301,813), auniform and fine dispersion of rubbery polymers in thermoplastics toform dry free-flowing powders has not been reported.

[0004] U.S. Pat. Nos. 3,824,208, 5,153,238, 5,391,594 and 5,412,014describe the incorporation of fillers such as silica in rubbery polymersto form compositions which exist as free-flowing particles. However, thesurface chemistry of the filler in some cases can result in degradationof the matrix polymer.

[0005] Conventional approaches for obtaining free-flowing powders withelastomeric components include the use of block copolymers, core-shellcopolymers or graft copolymers with thermoplastics. Copolymerization orgrafting of glassy/crystalline thermoplastic prevents agglomeration ofthe rubbery component and enables convenient addition of these impactmodifiers as free-flowing powders in extrusion equipment for meltprocessing. Such approaches however do not provide a cost effectivesolution for preparing free-flowing polymeric dispersions.

[0006] It is difficult, however, to prepare homogeneous blends ofrubbery polymers with other resins, owing to the relativeintractabilities of said rubbery polymers and the slow progress ofdispersion of said polymer in the blend. Examples of some alternativeapproaches for obtaining free-flowing powders include mixing adispersion of an organic thermoplastic polymer with an emulsion of asilicone resin as taught by Fuhr et al. in U.S. Pat. No. 5,100,958. Thismethod is once again not cost effective since it involves a subsequentadjustment of pH for coagulation followed by isolation and drying of thecoagulate. Another method proposed by Vaughn in U.S. Pat. No. 4,153,639involves mixing the resin and the rubbery additive (in this casesilicone gum) in a liquid medium having a component which vaporizesreadily. The liquid medium is contacted with flowing live steam in aconduit and the mixture is fed into a closed chamber from which thesuperheated, vaporized liquid components are removed and a particulateblend is extracted.

[0007] Other practical limitations in melt-melt blending ofthermoplastics with rubbery polymers include the inability to dispersethe rubber phase adequately in the thermoplastic melt using conventionalprocessing equipment due to excessive shear heating in extruders, forexample, and a morphological balance between drop break up (dispersion)and the subsequent coalescence of the dispersed particles.

[0008] Some applications like powder coating require the availability ofthe thermoplastic resin blend in a powdery form. One route for theformation of thermoplastic blend powders involves high temperature meltextrusion of the various melt components followed by grinding of thethermoplastic pellets to obtain a free-flowing powder. The ability todirectly form uniform thermoplastic blends with fine morphologies atlower processing temperatures can provide a direct, cost-effective andsimpler process.

SUMMARY OF THE INVENTION

[0009] The present invention facilitates the formation of polymer blendsas described herein above. In particular, it makes it possible toprepare blends which are solid and free-flowing, said blends comprisinghigh and often major proportions of rubbery materials such aspolyorganosiloxanes and synthetic elastomers, said blends alsocontaining another resinous constituent. Among the blends that can beproduced are those useful as products in their own right and thoseuseful as master batches suitable for incorporation as additives inother polymer compositions.

[0010] In one of its aspects, the present invention provides a methodfor preparing a blend, said blend comprising: a polyolefin-comprisingrubber (A) having at least one of a glass transition temperature(Tg_(a)) or a melting temperature (Tm_(a)), a polyphenylene ether (B)having at least one of a glass transition temperature (Tg_(b)) ormelting temperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A andB are amorphous, Tm_(a)<Tm_(b) when both polymers A and B arecrystalline, Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B iscrystalline, and Tm_(a)<Tg_(b) when polymer A is crystalline and polymerB is amorphous, which comprises intimately mixing said polymers at asuitable temperature between the lower of Tg_(a) and Tm_(a) and thevalue of Tg_(b), for a time and under shear conditions sufficient toconvert polymer A to dispersed particles coated with polymer B andproduce a free-flowing blend. Also provided is a composition prepared bythe aforementioned method.

DETAILED DESCRIPTION

[0011] In some embodiments the present invention provides a methodwherein Tg_(a) is below about 160° C., in other embodiments below about50° C., and in still other embodiments below about minus 10° C. In someembodiments the present invention provides a method wherein polymer B iscrystalline. In still other embodiments the present invention provides amethod wherein polymer B is amorphous and Tg_(b) is above about 100° C.It is generally known to those skilled in the art that many, but notall, polymers as commonly obtained comprise a mixture of amorphous andcrystalline fractions. In some particular polymers an amorphous phasepredominates, while in other particular polymers a crystalline phase mayprovide a significant fraction of the total polymer. In other particularembodiments polymer A and polymer B are typically immiscible andincompatible with each other.

[0012] Provided in yet another embodiment is a method wherein polymers Aand B are mixed in a rotary blade mixer at a blade tip velocity in therange of about 1,000-15,000 cm/sec.

[0013] In another embodiment the instant invention provides acomposition comprising a blend of polymer A having glass transitiontemperature (Tg_(a)) and/or a melting temperature (Tm_(a)), polymer Bhaving glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,said composition being produced by the process of intimately mixing saidpolymers at a suitable temperature between the lower of Tg_(a) andTm_(a) and the higher of Tg_(b) and Tm_(b), for a time and under shearconditions sufficient to convert polymer A to dispersed particles coatedwith polymer B and produce a free-flowing blend in the form of a powder.In still another embodiment the instant invention provides a compositioncomprising a blend of polymer A having glass transition temperature(Tg_(a)) and/or a melting temperature (Tm_(a)), polymer B having glasstransition temperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, said composition beingproduced by the process of intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a), and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend in the form of a powder. In various embodimentsblends of the present invention are produced in solid form with no needfor quenching or cooling said blend, as is typically necessary whenusing common melt processing equipment. In some particular embodimentsthe free-flowing blend is prepared by the method of the invention whichdoes not involve melting of polymer B. In other particular embodimentspolymer B may be plasticized, for example by mixing with at least oneother polymer or additive which is at least partly miscible with polymerB such that the Tg of the mixture is lower than the Tg of polymer Bitself, in which case the temperature range for preparing blends by thepresent method is at a suitable temperature between the lower of Tg_(a)and Tm_(a), and the value of Tg for the mixture of polymer B with atleast one other polymer or additive which is at least partly misciblewith polymer B. An example of a plasticized mixture of a polymer B is amixture of a polyphenylene ether such as poly-2,6-dimethyl-1,4-phenyleneether with a polystyrene, which mixture typically has a Tg in betweenthat of the polyphenylene ether and the polystyrene dependent upon,among other factors, the relative proportions of the two polymers in themixture.

[0014] The free-flowing powders prepared by the method of the presentinvention have a mean particle size in one embodiment in a range ofbetween about 50 microns and about 4000 microns, in another embodimentin a range of between about 100 microns and about 3000 microns, inanother embodiment in a range of between about 200 microns and about2000 microns, in another embodiment in a range of between about 200microns and about 1500 microns, in another embodiment in a range ofbetween about 250 microns and about 1200 microns, in another embodimentin a range of between about 300 microns and about 1000 microns, and instill another embodiment in a range of between about 400 microns andabout 900 microns. In a particular embodiment a free flowing powderblend may be distinguished from a pelletized extrudate made in a meltprocess which pellets typically have at least one dimension greater thanabout 4000 microns.

[0015] In some embodiments the present invention provides a compositionwherein Tg_(a) is below about 160° C., in other embodiments below about50° C., in other embodiments below about 0° C., in other embodimentsbelow about minus 10° C., in other embodiments below about minus 30° C.,in other embodiments below about minus 50° C., and in still otherembodiments below about minus 80° C. In some embodiments the presentinvention provides a composition wherein polymer B is crystalline. Instill other embodiments the present invention provides a compositionwherein polymer B is amorphous and Tg_(b) is above about 100° C.

[0016] In various embodiments the present invention provides a methodand composition wherein polymer A is a polyorganosiloxane, apolyurethane rubber, a polysulfide rubber, an epoxide rubber, or apolyolefin-comprising rubber. Within the present context apolyolefin-comprising rubber is a natural or synthetic rubbery (orelastomeric) polymer which comprises structural units derived from atleast one olefinic monomer, and includes natural rubber, polyisoprene,1,4-polyisoprene, cis-1,4-polyisoprene, epoxidized natural rubber,chlorinated natural rubber, grafted natural rubber, butadiene rubber,polybutadiene, ethylene-propylene rubber (sometimes known as EP rubber),ethylene-propylene-diene modified rubber (sometimes known as EPDMrubber), ethylene-vinyl actetate rubber, styrenebutadiene rubber,poly(butadiene-co-styrene), styrene-ethylene butylene-styrene rubber(SEBS), styrene-isoprene-styrene rubber, styrene-isoprene rubber,styreneisoprene-butadiene rubber, butyl rubber,poly(isobutylene-co-isoprene), nitrile rubber, hydrogenated nitrilerubber, poly(butadiene-co-acrylonitrile), chloroprene rubber,polychloroprene, neoprene, fluorocarbon elastomers, poly(vinylidenefluoride-cohexafluoropropene), acrylic rubbers, poly(ethyl acrylate),poly(butyl acrylate), poly(isobutyl acrylate), poly(n-butyl acrylate),ethyl acrylate copolymers with at least one other crosslinkable monomer,butyl acrylate copolymers with at least one other crosslinkable monomer,acrylate-butadiene rubber, ethylene-acrylic rubber, ethylenemethylacrylate rubber, polynorbornene, polydicyclopentadiene, polyoctenamer,chlorobutyl rubber, bromobutyl rubber, chlorinated polyethylene, andchlorosulfonated polyethylene. In addition, suitablepolyolefin-comprising rubber includes ethylene/alpha-olefin copolymerswherein the alpha-olefin is selected from the group consisting of C₃ toC₂₀ alpha olefins with some particular alpha-olefins being propylene,butene, hexene, and octene. Such copolymers are often synthesized usingmetallocene catalyst systems. Such polymers are commercially availablefrom a wide variety of sources.

[0017] In some particular embodiments polymer A comprises at least onepolyorganosiloxane, especially polydiorganosiloxanes. Examples ofpolydiorganosiloxanes include polydialkylsiloxanes such aspolydimethylsiloxane and their fluorinated derivatives such aspoly(trifluoropropylmethylsiloxane). Polydialkylsiloxanes modified atone or more chain-ends, such as vinyl-terminated polydimethylsiloxane,may also be employed.

[0018] Polymers useful as polymer B may be amorphous or crystalline.When amorphous, they are characterized by their Tg_(b) value; whencrystalline, the crystalline melting temperature (Tm_(b)) may be moresignificant. Thus, there is a temperature span in which the method ofthe invention may be conducted which is above the glass transitiontemperature (Tg_(a)) or melting point (Tm_(a)) of polymer A and belowthe higher of the glass transition temperature (Tg_(b)) or crystallinemelting temperature (Tm_(b)) of polymer B.

[0019] Illustrative polymers useful as polymer B include olefin polymerssuch as polyethylene and polypropylene, polycarbonates, bisphenol Apolycarbonate, poly(vinyl chloride), polyesters including thermoplasticaromatic polyesters such as poly(ethylene terephthalate),poly(trimethylene terephthalate), poly(cyclohexanedimethanolterephthalate), polyarylate, and poly(butylene terephthalate), andthermoplastic aliphatic polyesters such aspoly(1,4-cyclohexanedimethyl-1,4-cyclohexanedicarboxylate);vinylaromatic polymers including polystyrene and styrene-acrylonitrilecopolymers, polyphenylene ethers, polyimides (includingpolyetherimides), polyethersulfones, polyetherketones,polyetheretherketones, and polyarylene sulfides. In some embodimentspolymers useful as polymer B are those having glass transitiontemperatures above about 150° C. In particular embodiments polymersuseful as polymer B comprise polyphenylene ethers, such as, but notlimited to, poly(2,6-dimethyl-1,4-phenylene ether) andpoly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether).

[0020] Elastomeric examples of polymer A employed in embodiments of thepresent invention are those which have a relatively low glass transitiontemperature Tg_(a). The value of Tg_(a) is generally below about 25° C.and may be below 0° C. For example, polydiorganosiloxane gums useful inthe invention may have Tg values down to about minus 127° C. with amelting point of about minus 40° C. Polymer A typically has a highviscosity, in some embodiments in the range of about 500,000 to about20,000,000 centipoise at a shear rate on the order of 10 sec⁻¹, howeverpolymers having viscosities as low as 5,000 and above about 20,000,000may also be used. In some embodiments examples of polymer A have anumber average molecular weight of greater than about 10,000 and inother embodiments greater than about 20,000. In various embodimentselastomeric examples of polymer A have an oil swell value (as measuredby ASTM 2000-90) of in some embodiments greater than 120 volume % at 70°C., in other embodiments greater than 130 volume % at 70° C., in otherembodiments greater than 140 volume % at 70° C., in other embodiments ina range of between 2 and 80 volume % at 100° C., and in still otherembodiments in a range of between 3 and 110 volume % at 150° C. In someembodiments examples of polymer A have a Mooney viscosity in the rangeof between about 20 and about 100, in other embodiments in the range ofbetween about 20 and about 90, in other embodiments in the range ofbetween about 40 and about 90, and in still other embodiments in therange of between about 40 and about 70.

[0021] The compositions of the invention may include additives such asfillers, plasticizers, compatibilizers, lubricants, UV screeners, flameretardants, antistatic agents, antioxidants, and the like. In particularembodiments compositions may optionally include inorganic fillers suchas silica filler and treated silica filler. For some particularapplications it may be desirable for compositions of the invention toexclude inorganic fillers such as silica filler and treated silicafiller.

[0022] In a particular embodiment of the invention, polymers A and B aremixed under high shear conditions, at a temperature higher than Tg_(a)or Tm_(a) and lower than the higher of Tg_(b) and Tm_(b). In anotherparticular embodiment of the invention, polymers A and B are mixed underhigh shear conditions, at a temperature higher than Tg_(a) or Tm_(a) andlower than the value of Tg_(b). In another particular embodiment of theinvention, polymers A and B are mixed under high shear conditions, at atemperature higher than at least one of Tg_(a) or Tm_(a) and lower thanthe value of Tg_(b). Mixing is generally conducted in one or morediscrete steps rather than continuously as in an extruder, and underhigh shear conditions sufficient to produce a composition of the typedescribed hereinafter. High shear mixers of this type are known in theart and include Waring blenders, Henschel mixers, Drais mixers andmixer-granulators of the type manufactured by Littleford Bros.,Florence, Ky.

[0023] In general, both polymers are charged in their entirety beforemixing begins. It is within the scope of the invention, however, to addpolymer A and polymer B incrementally, so as to maintain conditionsunder which a dispersion of polymer A in solid polymer B is formed.

[0024] It has been shown in some embodiments that initially, adispersion of gum (polymer A) in solid (polymer B) is formed. During thehigh shear mixing process, a progressive breakdown of the particle sizeof polymer A occurs. Simultaneously, the particles of polymer B coatthose of polymer A to form a solid, particulate blend which is a soliddispersion of polymer A in polymer B and which is free-flowing attemperatures below the higher of Tg_(b) and Tm_(b).

[0025] The proportions of polymers A and B, as well as the mixing timeand conditions, are chosen to ensure that all particles of polymer A aredispersed and coated. If the mixing time is too long, polymer A willform particles so small that the quantity of polymer B will beinadequate to fully coat them, whereupon reagglomeration will take placeimmediately or upon storage.

[0026] Thus, suitable proportions and mixing conditions can bedetermined by simple experimentation. Weight ratios of polymer B topolymer A are in various embodiments in the range of about 1:1 to about5:1. In the case of a rotary blade mixer, blade tip velocities in therange of about 1,500 to about 15,000 cm/sec are generally adequate toproduce the required high shear mixing.

[0027] The blending temperature is not particularly critical. In oneembodiment the blending temperature is between the lower of Tg_(a) andTm_(a) and the higher of Tg_(b) and Tm_(b). In another embodiment theblending temperature is between the lower of Tg_(a)and Tm_(a) and thevalue of Tg_(b). In a particular embodiment where Tg_(a) is below about0° C. and Tg_(b) or Tm_(b) is above about 150° C., blending at moderatetemperatures in the range of about 20° C. to about 75° C., andespecially at ambient temperature of about 25° C., is satisfactory. Inother embodiments, polyethylene with a Tm of about 110° C. may beemployed as polymer A with a polyphenylene ether having a Tg of 210° C.as polymer B, if blending is at a temperature typically around 150° C.In various embodiments the blending temperature is below both Tg_(b) andTm_(b).

[0028] Following the blending operation of the present invention, it issometimes desirable to extrude and to pelletize the polymer blend of theinvention to form a storable material. Depending on the constituentsemployed, this storable material may itself be a useful polymercomposition or may be a master batch or an additive for incorporationinto other polymer compositions.

[0029] Without further elaboration, it is believed that one skilled inthe art can, using the description herein, utilize the present inventionto its fullest extent. The following examples are included to provideadditional guidance to those skilled in the art in practicing theclaimed invention. The examples provided are merely representative ofthe work that contributes to the teaching of the present application.Accordingly, these examples are not intended to limit the invention, asdefined in the appended claims, in any manner. All parts are by weight.

EXAMPLE 1

[0030] A mixture of 25 parts of a vinyl-terminated polydimethylsiloxanegum (Tg about minus 127° C. & Tm about minus 40° C.) having a viscosityof about 3.9 million centipoise at a shear rate of about 10.14 sec⁻¹ and100 parts of a poly(2,6-dimethyl-1,4-phenylene ether) having a Tg_(b) ofabout 210° C. having an intrinsic viscosity of 0.4 dl/g (in chloroformat 25° C.) was mixed at room temperature (about 25° C.) in a Waringblender at high speed for 10 minutes. The desired blend was obtained asa free-flowing powder, with 2.36 parts of unblended silicone remaining.The blend was capable of being molded, as shown by a compression moldingoperation at 300° C. Mixing time and shear rate are critical forcontrolling the amount of unblended silicone.

EXAMPLE 2

[0031] The procedure of Example 1 was repeated, except that mixing wasconducted in a Henschel mixer at a tip speed of 4,000 cm/s and ambienttemperature. The product was a free-flowing powder capable of extrusionand molding with no detectable unblended silicone.

EXAMPLE 3

[0032] The procedure of Example 2 was employed to prepare a free-flowingpowder of 4 parts of polyethylene powder (Tm_(b) about 120° C., andTg_(b) about minus 80° C.) and 1 part of methyl-stoppedpolydimethylsiloxane gum (Tg about minus 127° C. & Tm about minus 40°C.) having a viscosity of about 3,900,000 centipoise at 10.14 sec⁻¹. Theblend was capable of extrusion and molding.

EXAMPLE 4

[0033] The procedure of Example 3 was repeated, substituting 4 parts ofpolystyrene powder (Tg_(b) about 100° C.) for the polyethylene powder. Asimilar product was obtained.

EXAMPLE 5

[0034] The procedure of Example 4 was repeated, substituting 4 parts ofbisphenol A polycarbonate powder (Tg_(b) about 162° C.) for thepolyethylene powder. A similar product was obtained.

EXAMPLE 6

[0035] The procedure of Example 1 was repeated, using a blend of 1 parteach of the polyphenylene ether (Tg_(b) about 210° C.) and anethylene-propylene rubber (Tg_(a) about minus 80° C.). A well dispersed,free-flowing powder with a shelf life of at least one month wasobtained. The blend was capable of extrusion and molding.

[0036] While the invention has been illustrated and described in typicalembodiments, it is not intended to be limited to the details shown,since various modifications and substitutions can be made withoutdeparting in any way from the spirit of the present invention. As such,further modifications and equivalents of the invention herein disclosedmay occur to persons skilled in the art using no more than routineexperimentation, and all such modifications and equivalents are believedto be within the spirit and scope of the invention as defined by thefollowing claims. All U.S. Patents and U.S. Patent applications citedherein are incorporated herein by reference.

What is claimed is:
 1. A method for preparing a blend, said blendcomprising: a polyolefin-comprising rubber (A) having at least one of aglass transition temperature (Tg_(a)) or a melting temperature (Tm_(a)),a polyphenylene ether (B) having at least one of a glass transitiontemperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, which comprises intimatelymixing said polymers at a suitable temperature between the lower ofTg_(a) and Tm_(a) and the value of Tg_(b), for a time and under shearconditions sufficient to convert polymer A to dispersed particles coatedwith polymer B and produce a free-flowing blend.
 2. The method accordingto claim 1 wherein Tg_(a) is below about 160° C.
 3. The method accordingto claim 2 wherein Tg_(a) is below about 50° C.
 4. The method accordingto claim 3 wherein Tg_(a) is below about minus 10° C.
 5. The methodaccording to claim 2 wherein polymer B is crystalline.
 6. The methodaccording to claim 3 wherein polymer B is amorphous and Tg_(b) is aboveabout 100° C.
 7. The method according to claim 1 wherein thepolyolefin-comprising rubber comprises an ethylene-propylene rubber. 8.The method according to claim 1 wherein the polyphenylene ether (B)comprises a poly(2,6-dimethyl-1,4-phenylene ether).
 9. The methodaccording to claim 1 wherein said polymers are mixed in a rotary blademixer at a blade tip velocity in the range of about 1,000 to about15,000 cm/sec.
 10. The method of claim 1 wherein thepolyolefin-comprising rubber has a Mooney viscosity in a range ofbetween about 20 and about
 100. 11. A method for preparing a blend, saidblend consisting essentially of: an ethylene-propylene rubber (A) havingat least one of a glass transition temperature (Tg_(a)) or a meltingtemperature (Tm_(a)), a poly-2,6-dimethyl-1,4-phenylene ether (B) havingat least one of a glass transition temperature (Tg_(b)) or meltingtemperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B areamorphous, Tm_(a)<Tm_(b) when both polymers A and B are crystalline,Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B is crystalline,and Tm_(a)<Tg_(b) when polymer A is crystalline and polymer B isamorphous, which comprises intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend.
 12. A composition comprising a blend of: apolyolefin-comprising rubber (A) having at least one of a glasstransition temperature (Tg_(a)) or a melting temperature (Tm_(a)), apolyphenylene ether (B) having at least one of a glass transitiontemperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, produced by the process ofintimately mixing said polymers at a suitable temperature between thelower of Tg_(a) and Tm_(a) and the value of Tg_(b), for a time and undershear conditions sufficient to convert polymer A to dispersed particlescoated with polymer B and produce a free-flowing blend.
 13. Thecomposition according to claim 12 wherein Tg_(a) is below about 160° C.14. The composition according to claim 13 wherein Tg_(a) is below about50° C.
 15. The composition according to claim 14 wherein the Tg_(a) isbelow about minus 10° C.,
 16. The composition according to claim 12wherein polymer B is crystalline.
 17. The composition according to claim14 wherein polymer B is amorphous and Tg_(b) is above about 100° C. 18.The composition according to claim 12 wherein the polyolefin-comprisingrubber comprises an ethylene-propylene rubber.
 19. The compositionaccording to claim 12 wherein the polyphenylene ether (B) comprises apoly(2,6-dimethyl-1,4-phenylene ether).
 20. The composition of claim 12wherein said polymers are mixed in a rotary blade mixer at a blade tipvelocity in the range of about 1,000 to about 15,000 cm/sec.
 21. Thecomposition of claim 12 wherein the polyolefin-comprising rubber has aMooney viscosity in a range of between about 20 and about
 100. 22. Acomposition consisting essentially of a blend of: an ethylene-propylenerubber (A) having at least one of a glass transition temperature(Tg_(a)) or a melting temperature (Tm_(a)), apoly-2,6-dimethyl-1,4-phenylene ether (B) having at least one of a glasstransition temperature glass transition temperature (Tg_(b)) or amelting temperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A andB are amorphous, Tm_(a)<Tm_(b) when both polymers A and B arecrystalline, Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B iscrystalline, and Tm_(a)<Tg_(b) when polymer A is crystalline and polymerB is amorphous, produced by the process of intimately mixing saidpolymers at a suitable temperature between the lower of Tg_(a) andTm_(a) and the value of Tg_(b), for a time and under shear conditionssufficient to convert polymer A to dispersed particles coated withpolymer B and produce a free-flowing powder blend.